Field of the Invention
The present invention relates to a display device substrate capable of being applied with, for example, a touch sensing function or the like and a display device provided with a display device substrate. Further, the present invention is able to provide a display device substrate including a low reflectance electrode having low reflectance properties suitable for the display device and excellent light shielding properties for the transmitted light.
Discussion of the Background
Recently, in order to accomplish bright display and low power consumption, a high aperture ratio is required in a liquid crystal display device or an organic EL display device. According to these display devices, usually, a black matrix is used to divide pixels, improving the display contrast.
(Light Shielding Properties of Black Matrix)
A black matrix is arranged to surround pixels in order to secure the display contrast. Usually, to obtain light shielding properties, the black matrix is formed on a transparent substrate such as glass with a black resin where a colorant such as carbon is dispersed into a resin to have a film thickness of 1 μm. In particular, a frame portion provided on four sides in a periphery of the display portion where the plurality of pixels are arranged in matrix, that is, a black matrix formed in a frame shape, is required to have high light shielding properties such as an optical density of 5 or more or, or 6 or more, in the transmittance measurement. Light leakage of the backlight unit is likely to occur from the frame portion. Hence, the frame portion is required to have higher optical density than the black matrix formed on the display portion.
In addition to the high light shielding properties, the black matrix is required to have low reflectance to obtain high image quality or to improve its design. However, according to the black resin where a colorant such as carbon is dispersed into a resin, the more the content of carbon is increased, the higher the reflectance. Therefore, it has been hard to achieve high light shielding properties (high optical density) and low reflectance, and a black matrix having low film thickness.
(Thinning of Black Matrix)
In display devices of portable mobile equipment such as cellular phones, a thin black matrix is required due to a high-definition requirement e.g., 200 ppi or more and further 300 ppi or more. To obtain the black matrix with a high-definition quality, the pixel width becomes narrower, typically 30 μm or less. Accordingly, it has revealed that planarity of the color filters deteriorated due to the film thickness of the black matrix. The black matrix of a high-definition display device having a density of 300 ppi or more requires a thin pattern having a thickness of 4 μm or less.
For example, to enhance the light shielding properties of the black matrix, a black matrix having a thin pattern having a thickness of 4 μm or less is formed by a process where a photolithography step is performed for two times. Specifically, forming a black matrix having two layers is extremely difficult from the perspective of alignment. The formation of the black matrix with two step processes is likely to cause a change in width of lines and display unevenness due to an alignment error.
(Touch Sensing Function of Display Device)
As a method of directly inputting to a liquid crystal display device or an organic EL display device, there are methods in which an electrostatic capacitive type touch panel is attached to these display devices, and methods in which elements corresponding to the touch sensing function are provided in the display device. The latter is referred to as in-cell type method. The in-cell type method includes methods using an electrostatic capacitive type or an optical sensor.
According to the in-cell type touch sensing technique in which the display device itself allows inputs from a pointer such as fingers, electrostatic capacitive type is often used. In this electrostatic capacitive type method, two pairs of the plurality of electrode groups to detect electrostatic capacitance are required to detect electrostatic capacitance as disclosed in patent literatures 1 to 4.